1. Field of Invention
The present invention relates to a micromechanical resonator oscillator structure and its driving method. More particularly, the present invention relates to a micromechanical resonator oscillator and its high equivalent stiffness driving method.
2. Description of Related Art
A quartz crystal oscillator is used for generating clock pluses and widely used in electronic products such as mobile phones, personal computers, digital cameras, electronic clocks and motherboards. However, a conventional quartz crystal oscillator has the disadvantages of being bulky, costly and difficult to be integrated with IC (Integrated Circuit). Recently, the developments of the micromechanical resonator oscillator get more focused. The advantages of the micromechanical resonator oscillator are low cost, small volume and high integration capability to the LSI (Large-Scale-Integrated Circuits). The anti-shock capability of the micromechanical resonator oscillator is also better than that of the Quartz crystal oscillator.
U.S. Pat. No. 6,249,073 discloses a micromechanical oscillator structure. The micromechanical oscillator structure comprises a beam oscillator and a supporting structure. The supporting structure supports the beam oscillator in order to form a gap, thus forming an oscillation. The micromechanical oscillator can obtain a high Q-value in a high frequency range. Besides, the working frequency can be expanded by a differential signal technique.
U.S. Pat. No. 6,958,566 discloses another mechanical oscillator related to phenomena of dependent electronic stiffness. The mechanical oscillator o comprises a substrate, a mechanical oscillator and a supporting structure. A gap is formed between the nearby electrode and the mechanical oscillator. By means of a controllable voltage between an electrode and the mechanical oscillator, improvement on the instability of the oscillating frequency caused by temperature and acceleration can be made.
Although the prior art discloses a micromechanical oscillator structure and a driving method thereof, yet an issued of high phase noise still remains unsolved.